The present disclosure generally relates to a clear or substantially colorless overcoat composition that may be used for overcoating, for example, ink based images and xerographic images. The overcoat composition described herein is a clear solid ink which comprises one or more specific waxes that can be used in ink jet printing machines or printers. Also described is methods for using and stabilizing the overcoat composition.
In general, ink jet printing machines or printers include at least one printheard that ejects drops or jets of liquid ink onto a recording or image forming media. A phase change ink jet printer employes phase change inks that are in the solid phase at ambient temperature, but transition to a liquid phase at an elevated temperature. The molten ink can then be ejected onto a printing media by a printhead directly onto an image receiving substrate, or indirectly onto an intermediate imaging member before the image is transferred to an image receiving substrate. Once the ejected ink is on the image receiving substrate, the ink droplets quickly solidify to form an image. In both the direct and offset printing architecture, images may be formed on a media sheet or a media web.
Two difficulties faced in imaging devices, and in particular, imaging devices that utilize phase change ink to form images, are ink rub and offset during handling of the prints. As used herein, ink rub refers to the smearing or scuffing of the ink of an image on a receiving substrate, such as a sheet of paper. Ink offset refers to ink from an image formed on a surface or portion of a surface of a receiving substrate being transferred to another surface or another portion of the substrate. Ink rub and offset is particularly a concern for applications that require extensive handling such as the outside of envelopes or printed sheets inserted into envelopes.
To prevent ink rub and/or offset, some previously known systems have been implemented to apply a protective coating, such as disclosed in U.S. patent application Ser. No. 12/617,230, filed on Nov. 12, 2009, to David A. Mantell et al., over the printed image on the substrate to prevent or minimize ink rub or offset of the printed image. However, there is a continued desire to improve such known systems and methods of protecting ink or toner-based images to, for example, enhance performance of the protective coatings, maintain desired viscosity of the protective coating in the printer over a prolonged period of time so as to avoid clogging, or require less coverage to effect protection in order to reduce costs.
Thus, there remains a need for an overcoat composition that can be used for protecting solid ink and toner-based images, which provides overcoat coating properties including, for example, thermal and light stability, scratch resistance, and smear (or rub) resistance to toner-based images and ink-based images, particularly in commercial print applications, and which can be readily used in current printing systems.